linux-kernel - Re: [PATCH 2/2] leds: lp5024: Add the LP5024/18 RGB LED driver

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Date:   Mon, 7 Jan 2019 22:13:59 +0100
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Vesa Jääskeläinen <dachaac@...il.com>,
        Pavel Machek <pavel@....cz>
Cc:     Dan Murphy <dmurphy@...com>, robh+dt@...nel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-leds@...r.kernel.org
Subject: Re: [PATCH 2/2] leds: lp5024: Add the LP5024/18 RGB LED driver

Hi Vesa,

On 1/5/19 1:39 AM, Vesa Jääskeläinen wrote:
> Hi Jacek,
> 
> On 04/01/2019 23.37, Jacek Anaszewski wrote:
>> But, aside from that hypothetic issue, we need a solution for
>> LEDn_BRIGHTNESS feature of lp5024, i.e. setting color intensity
>> via a single register write. How would you propose to address that?
> 
> You could model it to something like this in device tree:
> 
> led-module @ <i2c-address> {
>      compatible = "lp5024";
> 
>      // There is in hardware setup to use either linear or
>      // logarithmic scaling:
>      //enable-logarithmic-brightness;
> 
>      led0 {
>          // this will create led instance for LED0 in lp5024
>          label = "lp-led0";
> 
>          // This specifies LED number within lp5024
>          led-index = <0>;   // set output-base as 0*3 == 0
> 
>          element-red {
>              // refers to OUT0
>              output-offset = <0>;
>          };
> 
>          element-green {
>              // refers to OUT1
>              output-offset = <1>;
>          };
> 
>          element-blue {
>              // refers to OUT2
>              output-offset = <2>;
>          };
> 
>      };
> 
>      led1 {
>          // this will create led instance for LED1 in lp5024
>          label = "lp-led1";
> 
>          // This specifies LED number within lp5024
>          led-index = <1>;   // set output-base as 1*3 == 3
> 
>          element-red {
>              // refers to OUT3
>              output-offset = <0>;
>          };
> 
>          element-green {
>              // refers to OUT4
>              output-offset = <1>;
>          };
> 
>          element-blue {
>              // refers to OUT5
>              output-offset = <2>;
>          };
> 
>      };
> 
>      bank-led {
>          // this will create led instance for bank leds in lp5024
>          label = "lp-bank-led";
> 
>          // configured bank led configuration
>          led-index = <2 3 4 5 6 7>;
>          // As here is list of led-indices this entry is
>          // assumed to be bank configuration. Bank mode is enable
>          // for the indices.
> 
>          // set output-base as BANK A
> 
>          element-red {
>              // refers to BANK A
>              output-offset = <0>;
>          };
> 
>          element-green {
>              // refers to BANK B
>              output-offset = <1>;
>          };
> 
>          element-blue {
>              // refers to BANK C
>              output-offset = <2>;
>          };
>      };
> };
> 
> This would then create three led instances and each led instance has 
> brightness setting and that goes straight to hardware.
> 
> If one would want to override hardware control for brightness then I 
> suppose you would define in led node something like:
> 
>      brightness-model = "hsl"
> 
> This would then pick red, green and blue elements for hsl calculations 
> and others color elements for linear. LED specific hardware brightness 
> would then be either 0 or 0xFF depending if all of LED color elements 
> are zero or not.
> 
> Would that kind of model work?

I'd prefer to have single RGB LED device. And your DT design
is unnecessarily complex and a bit confusing.

Also, you provided scarce information about sysfs interface.
It would be nice to see the sequence of commands.

-- 
Best regards,
Jacek Anaszewski